1. Technical Field of the Invention
The present invention relates to a cup-type plating apparatus for carrying out a plating treatment on a semiconductor wafer.
2. Description of the Related Art
Conventionally, there has been known and in practical use a cup-type plating apparatus for carrying out a plating treatment on a semiconductor wafer. Such a cup-type plating apparatus comprises a wafer support section provided along an upper opening of a plating tank, a plurality of plating-solution-outlet passages provided below the wafer support section and extending from the inside of the plating tank to the outside thereof, at least one plating-solution-supply pipe provided through the bottom of the plating tank. In detail, a plating solution supplied to the plating tank through the at least one plating-solution-supply pipe by virtue of an upward flow of the plating solution, is caused to form a plurality of outward flows passing through the plurality of plating-solution-outlet passages and thus arriving at the outside of the plating tank, while at the same time the plating solution is caused to contact a surface to be plated (the surface to be plated) of a wafer mounted on the wafer support section, to whereby effect a plating treatment on the wafer.
In fact, such a cup-type plating apparatus is so formed that the plating liquid can be supplied, by virtue of an upward flow of the plating solution, to the surface to be plated of the wafer. As a result, the plating solution is caused to contact the surface to be plated of the wafer, in a manner such that the plating solution flows radially from an area near the center of the surface to be plated towards its annular edge portion, thereby effecting a uniform plating treatment on the entire wafer surface to be plated. Then, since the plating treatment can be performed on a great number of wafers by successively replacing one treated wafer (mounted on the wafer support section) with an untreated one, the conventional plating apparatus has been widely and suitably used in various industrial processes, such as a small lot production or an automatic plating treatment.
However, in the conventional cup-type plating apparatus described in the above, since there is a small height difference between the plating-solution-outlet passages (provided under the wafer support section) on one hand and the surface to be plated of a wafer (mounted on the wafer support section) on the other, an undesired corner area is formed therebetween. As a result, a flow retardation of the plating solution will occur in the corner area, thus causing an ununiform plating on an annular edge portion of the wafer surface to be plated. Consequently, a semiconductor wafer treated in this way is greatly limited in its effectively usable area, resulting in an unsatisfactory yield in industrial production. In order to solve this problem, there has been a demand to develop an improved technique capable of effectively performing a uniform plating treatment on a wafer, so as to produce a plated wafer having an increased effectively usable area.
Further, with the development of a technique called fine wiring in recent years, a circuit to be formed on the surface of a wafer can be processed into an extremely fine pattern. Accordingly, there has been a demand to develop a technique capable of performing a uniform plating treatment on the surface of a wafer on which a fine wiring pattern has been formed.
However, in using the above described conventional cup-type plating apparatus, since the flowing state of the plating solution on the surface to be plated of a wafer is so formed that the plating solution will spread radially and constantly from an area near the center of the surface to be plated to the annular edge portion thereof, it is difficult to effect a uniform plating treatment on the entire surface to be plated having a fine wiring pattern formed thereon. Further, since it has been difficult to cover the entire wafer surface to be plated including its annular edge portion with plating solution, it has been also difficult to ensure a uniform plating treatment on a large area of a wafer.
In view of the above, this invention provides an improved cup-type plating apparatus capable of solving the problem of ununiform plating on the annular edge portion of a surface to be plated (the surface to be plated) of a wafer, which ununiform plating is usually caused due to an ununiform flow of a plating solution (when using a conventional cup-type plating apparatus), thereby ensuring a uniform plating treatment on the entire surface to be plated of the wafer.
In order to achieve the above object, the present invention provides a cup-type plating apparatus comprising a wafer support section provided along an upper opening of a plating tank, a plurality of solution-outlet passages provided below the wafer support section and extending from the inside of the plating tank to the outside thereof, and at least one solution-supply pipe provided through the bottom of the plating tank. In detail, a plating solution supplied through the at least one solution-supply pipe by virtue of an upward flow of the plating solution, is caused to form a plurality of outward flows passing through the solution-outlet passages and thus arriving at the outside of the plating tank, while at the same time the plating solution is rendered to contact a surface to be plated (the surface to be plated) of a wafer mounted on the wafer support section, to whereby carry out a plating treatment on the wafer. In particular, the plating apparatus of the present invention is characterized in that: below the surface to be plated of the wafer mounted on the wafer support section, there is provided a stirring device for effecting a forced agitation of the plating solution supplied into the plating tank.
In the conventional cup-type plating apparatus described in the above, since the plating solution supplied into the plating tank by virtue of its upward flow is caused to spread radially and constantly from an area near the center of the surface to be plated to the annular edge portion thereof, the concentration of metallic ions of the plating solution near the annular edge portion of the surface to be plated is likely to be different from that near the center of the same surface to be plated. Particularly, when an electric current density is increased, the nature of the plating treatment near the center of the surface to be plated will be different from that near the annular edge portion of the same surface to be plated, resulting in an ununiform plating treatment. In contrast, with the use of the cup-type plating apparatus of the present invention, an upward flow of the plating solution supplied through the at least one plating-solution-supply pipe will be changed in its flowing direction by virtue of the stirring device. Consequently, if viewed on the entire surface to be plated, the plating solution will be in a relatively random flowing state so as to get full contact with the surface to be plated of a wafer. Therefore, the metallic ions of the plating solution are allowed to be uniformly supplied to the entire surface to be plated of a wafer, thus effecting a plating treatment having an extremely high uniformity. Further, since the plating solution is in a relatively random flowing state when getting in contact with the surface to be plated, it is possible to avoid the occurrence of an ununiformly plated external appearance which would otherwise be caused due to an ununiform spreading of the plating solution.
Here, the stirring device of the present invention should not be limited to any specific type, provided that it can effect an agitation of the plating solution supplied to the plating tank by virtue of its upward flow. For example, a stirring blade having a plurality of impellers may be disposed below the surface to be plated of a wafer and can be rotated in this position. Alternatively, a pump device may be added to spray the plating solution so as to change the flowing state of the plating solution being supplied through the plating-solution-supply pipe. This means that any type of stirring device can be used to effect a desired agitation, provided that it can change the flowing state of the plating solution on the surface to be plated (such a flowing state is formed due to an upward flow of the plating solution being supplied hereto).
Specifically, in the cup-type plating apparatus formed according to the present invention, it is preferable that the stirring device comprises a doughnut-like disc having a plurality of stirring impellers capable of effecting a forced change of the flowing state of the plating solution flowing below and in the vicinity of the annular edge portion of the surface to be plated of the wafer, and a driving mechanism capable of supporting the doughnut-like disc in a manner such that the disc can be kept parallel to the surface to be plated of the wafer, and at the same time rotating the disc in a direction perpendicular to the upward flow of the plating solution being supplied through the at least one plating-solution-supply pipe.
In this way, the plating solution supplied to the plating tank by virtue of its upward flow is allowed to pass through the center opening of the doughnut-like disc so as to arrive at the surface to be plated of a wafer. Then, the flowing state of the plating solution spreading radially towards the annular edge portion of the surface to be plated of a wafer will be changed by the stirring blade. Therefore, it is possible to eliminate the flow retardation of the plating solution which would otherwise be caused due to a slight height difference between the plating-solution-outlet passages (provided below the wafer support section) on one hand and the surface to be plated of the wafer (mounted on the wafer support section) on the other, thereby making it possible to perform a uniform plating treatment on the entire surface to be plated including its annular edge portion.
The stirring blade may be of any type if it has a shape capable of effecting a forced change of the flowing state of the plating solution near and below the annular edge portion of the surface to be plated. Further, in order to more effectively change the flowing state of the plating solution on the surface to be plated of a wafer, it is more preferable that a stirring blade be located in the vicinity of the surface to be plated. Moreover, the shape and the area of the center opening of the doughnut-like disc may be made to be coincident with the position and the size of the plating-solution-supply pipe, provided that the plating solution supplied to the plating tank by virtue of its upward flow can arrive at the surface to be plated of a wafer mounted on the wafer support section.